Products of Caddis-Fly Larvae (Trichoptera) Silk Glands As a New

Marina Michalak, Mariusz Tszydel*, Products of Caddis-fly Larvae Trichoptera( ) Jadwiga Bilska, Izabella Krucińska Silk Glands as a New Natural Textile Fibre Technical University of Łódź, Abstract Department of Textile Marketing and Engineering, Among the invertebrates, some insects are able to produce natural silk fibres which can ul. Żeromskiego 116, 90-543 Łódź, Poland serve as an alternative to the threads of the spider’s web. The larvae of the caddis-fly [email protected] make use of a multifunctional silky floss in producing hunting nets and residential tubular structures. Many species of caddis-fly build their capture webs in fast-flowing rivers. *Department of Ecology and Vertebrate Zoology, Therefore we suggest that such fibres must be strong. However, these webs have been University of Łódź, studied and researched previously, taking into consideration the webs’ shape and the ul. Banacha 12/16, 90-237 Łódź, Poland geometry of the meshes. This paper presents preliminary results concerning some of the [email protected] web material’s morphological properties and tensile strength. We investigated the product of silk gland coming from Hydropsyche pellucidula, which is one of the most common caddisflies in Polish lowland rivers. Our researches proved that a cross-section of caddis- fly fibres is circular, with an average diameter of 10 µm. The mean tensile strength of the fibres investigated is 45 cN/tex (5.7⋅109 N/m2), and is comparable to the strength of most spider thread. Key words: natural silk fibers, silk gland, morphological properties, caddis-flies, tensile strength, Hydropsyche pellucidula. Caddis-fly larvae are similar to spiders, and detritus (unidentified, disintegrated butterflycaterpillars (e.g. silkworms) organic matter) can fall into it [19]. and blackflies (Simuliidae, Diptera) in their ability to produce a cocoon shell in Each species has its own web mesh the form of a multifunctional silky floss. shape and diameter, and the way the web Taking into account the variety of forms is mounted depends on environmental and versatility of silken products, it may conditions (Figure 3) [10]. be concluded the mastery of making co- coons is comparable in Trichoptera and Irrespective of hydrological conditions, Araneinae. webs are usually highly regular in their n Introduction mesh size and pattern (Figure 4). Insects are the most widely distributed The fact that the caddis-fly’s ability to The structure and shape of a web may and frequently the most abundant group spin silky floss was known in the past, also depend on temperature [6]. The of invertebrates in the world. They in- not only to biologolists, is confirmed by minimum temperature at which webs clude caddis-flies (Trichoptera), which the text: are built is also a characteristic feature are not a commonly known species. They “O what tangled webs the caddis weave, are merolimnic insects, whose larvae and when first they practise to deceive!” pupae, with few exceptions, prefer aquat- ‘Marmion, Sir Walter Scott, 1808. ic ecosystems, while the adults (imagos) a) are pharate stages. The larvae of caddis- Larvae of caddis-flies use a silky floss flies are found in all types of freshwater which is a product of their spinning and marine environments. glands (Figure 1) to build various ac- commodation structures. The ‘weaving’ is done by the elements of the mouthpart b) and not by the abdomen, as in the case of spiders, which makes it much more Figure 2. Simple structures in the form of precise. holes and hunting tunnels of caddis-flies: a) Lype reducta [9], b) Wormaldia occipi- RESEARCH ANDRESEARCH DEVELOPMENT – CURRENT PUBLICATIONS talis [16]. Some caddis-fly larvae build only simple structures: padded holes, corridors, hunting tunnels (Figure 2). The larvae can a) easily move inside them. Such holes may b) have continuations in the form of ‘signal- ling threads’, which inform the predatory caddis-flies about the prey that stumbles a) over the threads, or about intruders [5]. Others build fully-fledged webs. These b) have a shape of a tunnel-like sieve, inside which the caddis-fly awaits its prey. The Figure 1. Location of spinning glands: inlet of such a structure is always directed a) in the body of the caddis-fly Neureclipsis Figure 3. Web shape of Hydropsyche bimaculata, b) the opening of silk glands at against the water current, so not only live angustipennis, depending on the substratum: the haustellum [2]. organisms but also fragments of plants a) plant [13], b) stone [19]. 28 FIBRES & TEXTILES in Eastern Europe January / December 2005, Vol. 13, No. 6 (54) FIBRES & TEXTILES in Eastern Europe January / December 2005, Vol. 13, No. 6 (54) 29 build their webs in river currents. They a) are usually stretched between aquatic b) plants, mainly submerged macrophytes or floating leaves (Figure 6). The most spectacular builder in this family is Plectrocnemia conspersa. We know [26] at least three types of webs built by c) P. conspersa, depending on water depth and velocity. In rivers of fast current, the web resembles a –‘swallow’s nest’ length of mesh width of mesh (Figure 7a), and a ‘hammock’ in shallow streams (up to 5 cm deep) (Figure 7b). In d) area of mesh deeper rivers the web is placed on the bottom, with the funnel-like openings turned Figure 6. Different types of webs and web- Figure 4. Web of caddis-fly larvae of the upwards, in this way catching victims houses of caddis-fly larvae from the family genus Hydropsyche [20]. moving along the bottom (invertebrates) Polycentropodidae: a) Holocentropus or settling organic matter (Figure 7c). dubius, b) Cyrnus flavidus, c) and d) N. bimaculata. a and b [23], c [13], d [2]. Using the silky floss to build a web is not this fabric’s only application. Without the floss, it would be impossible to form another characteristic structure, the house. a) Usually, the larva begins building its house by spinning a silky tubular structure, into which it builds elements forming the house (Figure 8): fragments of plants, detritus, sand, small stones and so on [14, 21, 15]. A strong floss and an organic or inorganic substrate are also the basic components b) of the house built for the pupa (Figure 9 - see page 30). All types of caddis-flies, in the fifth larval stage, start building this, because without the cocoon it would be im- c) possible for the specimen to metamorphose into the later stage. Figure 7. Different types of webs made by Caddis-fly larvae usually build their webs P. conspersa depending on environmental conditions in running waters: a. fast-mov- in fast-flowing rivers, and so the cocoon ing river, b. shallow river, c. deep river [5]. shell they produce must be strong. The product of Trichoptera’s spinning (silk) glands could be an alternative to a Figure 5. Scheme of web building by spider’s floss. Unlike spiders, caddis-flies caddisfly H. angustipennis [19]. fairly often produce cocoon shells in man- made conditions. It is much easier to breed for a given species (in low temperatures them, because cannibalism among them RESEARCH ANDRESEARCH DEVELOPMENT – CURRENT PUBLICATIONS some Hydropsychidae species, e.g. is not observed, which does happen in H. angustipennis, do not build webs) spiders (Arachnida). Unfortunately, we do [18]. However, web building always con- not find much significant data in literature sists of a set of similar actions, which are on the properties of fibres made by cad- shown in Figure 5. dis-flies. Therefore the aim of the studies that have been undertaken is to analyse One of the most impressive webs, tubu- the physical-mechanical properties, com- lar in shape, is built by N. bimaculata position and chemical structure of the (Polycentropodidae); it may be 20 cm cocoon shell which these insects produce. long, whereas the larva itself is no longer than 2 cm. Despite being so big, its mesh n is incredibly small, 0.45×0.45 µm; this is Study material one of the denser webs built by caddis- For microscopy observations, samples Figure 8. The course of the initial phase of flies [17]. Larvae of the family Polycen- were selected for the present studies from house-building whose construction requires tropodidae, with a few exceptions, do not different types of cocoon shell made by the product of spinning glands [16]. 28 FIBRES & TEXTILES in Eastern Europe January / December 2005, Vol. 13, No. 6 (54) FIBRES & TEXTILES in Eastern Europe January / December 2005, Vol. 13, No. 6 (54) 29 sary to determine the linear density of the fibres studied. In order to do this, after determining the breaking force and elon- gation, the broken parts of the fibres were placed on a micro-slide in an alcoholic medium, and then under the microscope; the crosswise dimensions of fibres were determined. In this case a Lanametr pro- jection microscope was used. The value of the crosswise dimension as determined by an optical method was considered on the fibre diameter. The mean diameter dav was determined for each fibre on the basis of 20 measurements. Later, its linear Figure 9. Pupal case and the structure of floss weave in the cocoon of larva Rhyacophila density Tt was calculated. subovata [13]. n Results Table 1. Tensile properties of Caddisfly fibres. Microscopy observations No. of F, cN ε, % σ, cN/tex L, cN cm d , µm Tt, tex sample av Images of fibres taken from the studied 1 10.31 23.8 26.2 2.45 25 0.393 samples are presented in Figures 10a - 2 5.40 16.0 21.5 0.86 20 0.251 10g. They were registered on the stand 3 5.40 18.0 21.5 0.97 20 0.251 for computer image analysis.

Load more